(1) Field of the Invention
The present invention relates to a novel seamless cylindrical printing screen. More particularly, the invention relates to a seamless cylindrical screen having a novel structure, which comprises a metal wire net substrate in which all the crossing points are fixed by a plating layer and which has a match higher aperture ratio than in conventional cylindrical screens, and also to a process for the manufacture of such seamless cylindrical screen.
(2) Description of the Prior Art
A printing process in which the printing operation is carried out while driving and rotating a cylindrical screen synchronously with a material to be printed is known. This printing process is advantageous over a so-called flat screen printing process with respect to the printing equipment and operation. For example, the structure of the printing equipment is relatively simple and the printing operation is carried out while a material to be printed is being continuously fed. However, this cylindrical screen printing process is disadvantageous as compared with the printing process using a flat screen with respect to the quality of printed products.
In the cylindrical screen printing process, the printing operation must be conducted while the cylindrical screen is being driven and rotated. Accordingly, it is required that the mesh structure of the cylindrical screen should have higher strength and rigidity than in a flat screen. Therefore, the aperture ratio (the ratio of the open aperture area to the total area) of the cylindrical screen is inevitably much lower than that of the flat screen. When the aperture ratio is low, the quality of printed products is degraded for the following reasons.
(1) Since the viscosity of a printing paste or ink or a vinyl chloride resin paste, must be maintained at a low level, the clarity of the color formed by printing is low, and the amount of the printing ink or vinyl chloride resin paste applied per unit area is small.
(2) the sharpness of the printed pattern is low and in some case, a line is printed in a saw tooth-like shape. Furthermore, contours become fuzzy and get blurred. Accordingly, it is very difficult to reproduce a fine and delicate pattern.
Therefore, in the art of the rotary screen printing, development of a printing cylinder having a high aperture ratio has been eagerly desired.
Furthermore, in the printing process using a vinyl chloride resin paste, it is desired to use a cylinder having a larger thickness and a higher aperture ratio. Conventional cylinders, however, are defective in that if the thickness is increased, the aperture ratio is proportionally lowered.
Cylindrical screens formed by subjecting an embossed surface of a mother roll, that is, a meshed, electrically conductive surface of a mother roll, to nickel plating and drawing out a meshed cylinder formed as a plating layer from the mother roll have been widely used as the cylindrical screens in the rotary screen printing process. In cylinder screens of this type, however, since the rate of growth of the plating layer on the surface of the mother roll in the plane direction is two times the growth rate of the plating layer in the thickness direction, the mesh width becomes much larger than the mesh thickness and the aperture ratio is very low as shown below:
60 mesh: 10 to 20% PA0 80 mesh: 6 to 10% PA0 100 mesh: 3 to 7% PA0 120 mesh: 3 to 5% PA0 74 mesh: about 20% PA0 107 mesh: about 15% PA0 143 mesh: about 11%
As another known cylindrical screen, there can be mentioned a meshed cylinder prepared by forming a metal layer by non-electrolytic plating on a tubular woven fabric composed of, for example, polyester fibers and forming a metal plating layer on this metal layer by electrolytic plating. This preparation method, however, is defective in that non-electrolytic plating and electrolytic plating, which are expensive and troublesome operations, should be performed. Moreover, in cylindrical screens of this type, it is difficult to maintain a mechanical or dimensional precision at a high level. Although the aperture ratio is improved in cylindrical screens of this type over the aperture ratio in cylindrical screens formed by performing the plating operation on the surface of a mother roll, the aperture ratio is still insufficient and low as shown below:
Cylindrical screens formed by winding a plain-weave metal net in the cylindrical form and butt-welding or fusion-bonding the lapped portion of the net are also known. Cylindrical screens of this type, however, have a fatal defect that because of the presence of a seam, continuous patterns cannot be printed.